(Shrug) They've already appealed the Competition Commission's ruling to the Supreme Court and lost; I doubt that an application for judicial review is likely to be any more successful. Still, if BAA wants to continue enriching m' learned friends....
Spin the process out for another two years until 2013, and then BAA can try to argue that the ruling from the Competition Commission from 2009 is out of date as it will by then be based on market conditions that were 4 years old, and thus is invalid.
Alternatively, (assuming Greece / Portugal / Ireland / Spain / Italy or the euro don't implode financially), the economy might have picked up a bit more and some other airport operator will pay a better price.
Of course all the time that BAA retain control of STN, they still have the capacity to exert more control and pricing power over any airline wishing to fly to a London airport. The more control they have over the market, the better likelihood of being able to charge higher fees
Difficult to see any incentive for BAA to get on with selling STN when delaying has a half decent chance of helping them